Experimental colitis modulates the functional properties of NMDA receptors in dorsal root ganglia neurons

University of Florence, Florens, Tuscany, Italy
AJP Gastrointestinal and Liver Physiology (Impact Factor: 3.8). 09/2006; 291(2):G219-28. DOI: 10.1152/ajpgi.00097.2006
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N-methyl-D-aspartate (NMDA) receptors (NMDARs) on spinal afferent neurons regulate the peripheral and central release of neuropeptides involved in the development of hyperalgesia. We examined the effect of experimental colitis on the molecular and functional properties of NMDARs on these neurons. Lumbosacral dorsal root ganglia (DRG) were collected from adult rats 5 days after the induction of colitis for whole cell patch-clamp recording, Western blot analysis, and quantitative RT-PCR. Compared with neurons from control rats, those taken from animals with colitis had a threefold higher density of NMDA currents in both retrograde-labeled, colon-specific, and unlabeled DRG neurons. Increased current densities were not observed in DRG neurons taken from thoracic spinal levels. There was no significant change in NMDA or glycine affinity or in voltage-dependent Mg2+ inhibition; however, there was a 10-fold decrease in sensitivity to the NR2B subunit-selective antagonist ifenprodil. Quantitative RT-PCR and Western blot analysis indicated a 28% increase in the expression of NR2B with little or no change in the other three NR2 subunits. The addition of the Src family tyrosine kinase inhibitor PP2 (10 microM) decreased NMDAR currents in neurons from colitis but not control rats. Conversely, pretreatment of DRG neurons from control animals with 100 microM sodium orthovanadate increased NMDAR currents and decreased ifenprodil sensitivity to levels similar to those observed in neurons from animals with colitis. In conclusion, colonic inflammation upregulates the activity of NMDARs in all DRG neurons within ganglia innervating this tissue through mechanisms involving increased expression and persistent tyrosine phosphorylation.

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Available from: Marcello Trevisani, Sep 29, 2015
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    • "This potentiation of NMDA receptors in primary afferents probably occurs in chronic pain disorders other than neuropathic pain. Thus, in a rat model of colitis there was an increase in NMDA receptor currents in DRG neurons mediated by SFKs (Li et al., 2006). Perhaps this can explain why Liu et al. (1997) found that intrathecal NMDA induced NK1R internalization: an undetected inflammation in their rats could have potentiated these NMDA receptors. "
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    ABSTRACT: NMDA receptors in primary afferent terminals can contribute to hyperalgesia by increasing neurotransmitter release. In rats and mice, we found that the ability of intrathecal NMDA to induce neurokinin 1 receptor (NK1R) internalization (a measure of substance P release) required a previous injection of BDNF. Selective knock-down of NMDA receptors in primary afferents decreased NMDA-induced NK1R internalization, confirming the presynaptic location of these receptors. The effect of BDNF was mediated by tropomyosin-related kinase B (trkB) receptors and not p75 neurotrophin receptors (p75(NTR) ), because it was not produced by proBDNF and was inhibited by the trkB antagonist ANA-12 but not by the p75(NTR) inhibitor TAT-Pep5. These effects are probably mediated through the truncated form of the trkB receptor as there is little expression of full-length trkB in dorsal root ganglion (DRG) neurons. Src family kinase inhibitors blocked the effect of BDNF, suggesting that trkB receptors promote the activation of these NMDA receptors by Src family kinase phosphorylation. Western blots of cultured DRG neurons revealed that BDNF increased Tyr(1472) phosphorylation of the NR2B subunit of the NMDA receptor, known to have a potentiating effect. Patch-clamp recordings showed that BDNF, but not proBDNF, increased NMDA receptor currents in cultured DRG neurons. NMDA-induced NK1R internalization was also enabled in a neuropathic pain model or by activating dorsal horn microglia with lipopolysaccharide. These effects were decreased by a BDNF scavenger, a trkB receptor antagonist and a Src family kinase inhibitor, indicating that BDNF released by microglia potentiates NMDA receptors in primary afferents during neuropathic pain.
    European Journal of Neuroscience 03/2014; 39(9). DOI:10.1111/ejn.12516 · 3.18 Impact Factor
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    • "Peripheral NMDARs are targets for the treatment of neuropathic pain (Wu & Zhuo, 2009). NMDARs expressed on spinal afferent neurons are upregulated in the lumbosacral dorsal root ganglia (DRG) following experimental colitis (Li et al., 2006). Peripheral NMDARs play a role in behavioral pain responses to colonic distention, suggesting that these receptors are important in visceral pain transmission (McRoberts et al., 2001). "
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    ABSTRACT: A recent study--comparing those with depression, somatization, comorbid depression+somatization, and controls--showed specific changes in the tryptophan catabolite (TRYCAT) pathway in somatization, specifically lowered tryptophan and kynurenic acid, and increased kynurenine/kynurenic acid (KY/KA) and kynurenine/tryptophan ratios. These findings suggest that somatization and depression with somatization are characterized by increased activity of indoleamine 2,3-dioxygenase and disorders in kynurenine aminotransferase activity, which carry a neurotoxic potential. This chapter reviews the evidence that the TRYCAT pathway may play a pathophysiological role in the onset of somatization and depression with somatization and, furthermore, suggests treatment options based on identified pathophysiological processes. Lowered plasma tryptophan may be associated with enhanced pain, autonomic nervous system responses, gut motility, peripheral nerve function, ventilation, and cardiac dysfunctions. The imbalance in the KY/KA ratio may increase pain, intestinal hypermotility, and peripheral neuropathy through effects of KY and KA acid, both centrally and peripherally, at the N-methyl-d-aspartate receptor (NMDAR), G-protein-coupled receptor-35 (GPR35), and aryl hydrocarbon receptor (AHr). These alterations in the TRYCAT pathway in somatization and depression may interface with the role of the mu-opioid, serotonin, and oxytocin systems in the regulation of stress reactions and early attachment. It is hypothesized that irregular parenting and insecure attachment paralleled by chronic stress play a key role in the expression of variations in the TRYCAT pathway-both centrally and peripherally-driving the etiology of somatization through interactions with the mu-opioid receptors. Therefore, the TRYCAT pathway, NMDARs, GPR35, and AHrs may be new drug targets in somatization and depression with somatizing. We lastly review new pathophysiologically driven drug candidates for somatization, including St. John's wort, resveratrol, melatonin, agomelatine, Garcinia mangostana (γ-mangostin), N-acetyl cysteine, and pamoic acid.
    07/2012; 88:27-48. DOI:10.1016/B978-0-12-398314-5.00002-7
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    • "Glutamate receptor activation mediates colonic inflammation [17, 18] as well as CNS events that mediate hyperalgesia [16]. Thus, the relative role of the anti-inflammatory effects of decreased glutamatergic tone by GLT-1 overexpression was explored. "
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    ABSTRACT: Visceral pain is the most common reason for physician visits in US. Glutamate is the major excitatory neurotransmitter and mediates visceral nociceptive neuro-transmission and hypersensitivity. Removal of extracellular glutamate is predominantly mediated by glial glutamate transporter-1 (GLT-1). The pharmacological approach to up-regulate GLT-1 by 1 week administration of ceftriaxone (CTX) has been successful to mitigate visceral nociception. The present study shows that intrathecal delivery of selective GLT-1 antagonist dihydrokainate reversed CTX-blunted visceral nociceptive response, suggesting a spinal site of action. The role of GLT-1 up-regulation in animal models of colitis was studied. CTX treatment reversed TNBS-induced visceral hypersensitivity. In addition, CTX treatment initiated one week after the onset of DSS-induced visceral inflammation also attenuated visceral hypersensitivity, revealing a potential therapeutic effect. Cephalothin, a cephalosporin antibiotic lacking GLT-1 induction activity, failed to attenuate visceral nociception. CTX-induced changes in fecal microbiota do not support a role of probiotic effects in mitigating visceral nociception/hypersensitivity. Finally, adeno-associated virus serotype 9-mediated GLT-1 over-expression was effective to mitigate visceromotor response to 60 mmHg colo-rectal distension. These studies indicate that GLT-1 over-expression is a novel and effective method to attenuate visceral nociception, and is deserving of further study as a translationally relevant approach to treat visceral pain.
    Pain Research and Treatment 12/2011; 2011(2-3):507029. DOI:10.1155/2011/507029
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